Process for coating glass

ABSTRACT

A process for the production of durable photocatalytically active self-cleaning coating on glass by contacting a hot glass surface with a fluid mixture of titanium chloride, a source of oxygen and a tin precursor. The coating preferably comprises less than 10 atom % tin in the bulk of the coating and preferably there is a greater atomic percent tin in the surface of the coating than there is in the bulk of the coating. Preferably, the coating is durable to abrasion and humidity cycling.

TECHNICAL FIELD

[0001] The present invention relates to a process for the production ofa durable photocatalytically active self-cleaning coated glass. Inparticular the present invention relates to a process for depositing adurable, photocatalytically active self-cleaning coating of titaniumoxide containing tin on the surface of a glass substrate. The presentinvention also relates to a durable, photocatalytically active coatedglass having a coating comprising titanium oxide containing tin.

BACKGROUND ART

[0002] It is known to deposit thin coatings having one or more layerswith a variety of properties on to glass substrates. One property ofinterest is photocatalytic activity which arises by photogeneration, ina semi-conductor, of a hole-election pair when the semi- conductor isilluminated by light of a particular frequency. The hole-electron paircan be generated in sunlight and can react in humid air to form hydroxyand peroxy radicals on the surface of the semi-conductor. The radicalsoxidise organic grime on the surface which both cleans the surface andincreases the hydrophilic properties (i.e. wettability) of the surface.A hydrophilic surface is beneficial because water will wet the surfacebetter, making the surface easier to clean with water containing littleor no detergent. In addition, water droplets will spread over thesurface reducing the distracting visual effects of rain or spray. Thus,photocatalytically active coated glass has a use in self-cleaning glassfor windows.

[0003] Titanium dioxide may be deposited on to glass to form atransparent coating with photocatalytic properties. In WO 98/06675 achemical vapour deposition process is described for depositing titaniumoxide coatings on hot flat glass at high deposition rate. In EP 901 991A2 a photocatalytically active titanium oxide coating deposited by DVDis disclosed.

[0004] Mixed oxide coatings of titanium with other metals are known. InGB 2 275 691 a glass substrate having a pyrolytically formed coating isdescribed, characterised in that the coating comprises tin oxide andtitanium oxide. The coating may be formed by contacting a hot glasssubstrate with a titanium containing precursor being the reactionproduct of octyleneglycol titanate and acetylacetonate together with atin-containing coating precursor, for example tin dibutyl/diacetate.Similar mixed titanium/tin oxide coatings are disclosed in GB 2150044and U.S. Pat. No. 4,687,687.

[0005] In WO 95/15816 sol gel processes for producing photocatalyticallyactive titanium oxide coatings which contain tin oxide particles aredescribed.

[0006] In WO 98/10186 it is stated that a photocatalytically activecoating may contain one other type of mineral material for example anoxide of silicon (or mixture of oxides) of titanium, tin, zirconium oraluminium. It has been suggested in WO98/10186 that mixed oxidescoatings containing titanium oxide or titanium oxide coatings may haveadvantageous optical properties for example by lowering the refractiveindex of the coating.

[0007] A problem arises with known photocatalytically active coatingsbased on titania in that the durability of the coating, especially toabrasion, may be poor. This is especially problematic because suchcoatings will often be used for their self-cleaning property and thisuse requires the coating to be on the outside surface of e.g. glazingswhere the coating may be particularly prone to abrasion.

[0008] The applicants have discovered that this problem may be addressedby depositing a titania coating containing tin on hot glass from a fluidcontaining a titanium precursor and a tin precursor.

DISCLOSURE OF INVENTION

[0009] The present invention accordingly provides a process for theproduction of a durable photocatalytically active self-cleaning coatedglass comprising contacting the surface of a hot glass substrate with afluid mixture comprising titanium chloride, a source of oxygen and a tinprecursor thereby depositing a tin containing titanium oxide coating onthe surface of the glass substrate.

[0010] Coated glasses produced by the process of the invention havesurprisingly high durability, both to abrasion (as determined forexample, by the European standard abrasion test as described in BritishStandard BS EN 1096 (Part 2, 1999)), and to temperature cycling in ahumid atmosphere. Preferably, the coated glass is durable to abrasionsuch that the coated surface retains a photocatalytic activity afterbeing subjected to 500 strokes of the European standard abrasion test.

[0011] Preferably, at least part of the fluid mixture contacts thesurface of the glass substrate by flowing over the surface of the glasssubstrate or, more preferably, by flowing over the surface of a glasssubstrate which is moving relative to the coating apparatus.

[0012] The preferred titanium chloride comprises titanium tetrachloridebecause it is relatively cheap, obtainable in pure form and volatile(allowing good carry over to the glass surface). However, generally anytitanium precursor having a chloro substituent may be used in theprocess of the invention.

[0013] Preferably, the tin precursor comprises a tin halide (i.e. a tincompound having a halo substituent), more preferably the tin precursorcomprises a tin chloride and most preferably the tin precursor comprisesdimethyl tin dichloride ((CH₃)₂ Sn Cl₂, DMT) or tin tetrachloride (SnCl₄). This is advantageous because these tin precursors are relativelycheap in bulk, obtainable in pure form and provide good carryover to theglass surface during deposition of the coating.

[0014] The source of oxygen preferably comprises an ester, especially acarboxylic acid ester. Usually, the ester will comprise a C₁ to C₄acetate because these esters are relatively volatile providingrelatively efficient incorporation of the ester in a carrier gas stream(this may be done, for example, by bubbling the carrier gas through theliquid ester). Most preferably the ester comprises ethyl acetate whichis cheap and has low toxicity.

[0015] Usually, the glass substrate will comprise a soda-lime-silicateglass substrate.

[0016] If the glass substrate comprises a soda-lime-silicate glasssubstrate or another glass substrate comprising alkali metal ions, theprocess of the invention preferably further comprises depositing analkali metal ion blocking underlayer on the surface of the glasssubstrate before depositing the coating of titanium oxide containingtin. This is advantageous because an alkali metal ion blockingunderlayer reduces migration of alkali metal ions from the glasssubstrate into the photocatalytically active coating which could reducethe photocatalytic activity of the coating and/or generate haze.Preferred alkali metal ion blocking underlayers comprise a silicon oxidelayer (which has similar retractive index to the glass substrate and sohas little effect on the optical properties of the coated glass) or adouble layer of tin oxide and silicon oxide. Alternatively, other alkalimetal ion blocking layers known in the art may be used if desired.

[0017] The photocatalytically active coating may be deposited usingspray deposition (in which the fluid mixture comprises liquid droplets)or chemical vapour deposition (CVD, in which the fluid mixture comprisesa gaseous mixture). The preferred deposition process is CVD, thus,preferably the fluid mixture comprises a gaseous mixture.

[0018] Usually, the hot glass substrate will be at a temperature in therage 500° C. to 750° C. which has been found in practice to be anespecially suitable temperature range for depositing durablephotocatalytically active coatings comprising titania.

[0019] At temperatures much lower than this the photocatalytic activityof coatings based on titania begins to drop off. At higher temperaturessome kinds of glass (including soda-lime-silicate glass) may begin tosoften. Preferably the hot glass substrate is at a temperature in therange 570° C. to 650° C.

[0020] The process will usually be performed at substantiallyatmospheric pressure.

[0021] It is advantageous if the process is performed during the floatglass production process because this is especially suitable forproducing large volumes of coated glass. In this case the process ispreferably performed in the float bath.

[0022] In preferred embodiments of the invention the amount of tin inthe bulk of the tin containing titanium oxide coating is below about 10atom % (as determined by X-ray photoelectron spectroscopy, XPS),preferably below about 5 atom % and more preferably below about 2 atom%. At higher amounts of tin, there may be a reduction in photocatalyticactivity of the coated glass. The amount of tin in the bulk of thecoating will usually be above about 0.05 atom %. Thus, preferably theamount of tin in the bulk of the coating is in the range 0.05 atom % to10 atom %, more preferably in the range 0.05 atom % to 5 atom % and mostpreferably in the range 0.05 atom % to 2 atom %. Thus, in anotheraspect, the present invention provides a process for depositing a tincontaining titanium oxide coating on the surface of a hot glasssubstrate comprising contacting the surface of the glass substrate witha fluid mixture comprising a titanium precursor, a source of oxygen anda tin precursor characterised in that the amount of tin in the bulk ofthe tin containing titanium oxide coating is below 10 atom %. The tincontent of the coatings appears to provide or contribute to thesurprisingly high durability of coatings deposited according to theinvention.

[0023] The applicants have unexpectedly discovered that in tincontaining titanium oxide coatings deposited according to the invention,there is a greater atomic percent tin in the surface of the tincontaining titanium oxide coating than there is in the bulk of thecoating. This may be advantageous in providing greater increase indurability for a relatively small amount of tin since durability toabrasion, humidity or other factors is likely to depend most on thesurface of a coating. The surface of the coating normally meansapproximately 10% of the thickness of the coating in terms of the totalcoating thickness.

[0024] Preferably, the atomic percent tin in the surface of the tincontaining titanium oxide coating is at least twice that in the bulk ofthe coating.

[0025] The present invention provides in a further aspect a durable,photocatalytically active coated glass comprising a glass substratehaving a coating comprising tin containing titanium oxide, the amount oftin in the bulk of the coating being below 10 atom %. The atomic percenttin in the surface of the coating is preferably at least twice that inthe bulk of the coating, and is preferably above 0.05 atom %.

[0026] Coated glasses according to the invention have uses in many areasof glass use including as glazings in buildings (either in singleglazing, multiple glazing or laminated glazing) or in vehicles (eitherin laminated glazings or otherwise).

[0027] Preferably, coated glasses according to the invention will havevalues of visible reflection measured on the coated side of 25% orlower, more preferably of 20% or lower and most preferably of 15% orlower.

[0028] Coated glasses according to the invention are photocatalyticallyactive which is advantageous because the amount of contaminants(including dirt) on the coated surface of the photocatalytically activecoated substrate will be reduced if the surface is illuminated by UVlight (including sunlight).

[0029] Preferably, the coated glass has a static water contact angle (onthe coated side) of 20° or lower. The static water contact angle is theangle subtended by the meniscus of a water droplet on a glass surfaceand may be determined in a known manner by measuring the diameter of awater droplet of known volume on a glass surface and calculated using aniterative procedure. Freshly prepared or cleaned glass has a hydrophilicsurface (a static water contact angle of lower than about 40° indicatesa hydrophilic surface), but organic contaminants rapidly adhere to thesurface increasing the contact angle. A particular benefit of coatedglasses of the present invention is that even if the coated surface issoiled, irradiation of the coated surface by UV light of the rightwavelength will reduce the contact angle by reducing or destroying thosecontaminants. A further advantage is that water will spread out over thelow contact angle surface reducing the distracting effect of droplets ofwater on the surface (e.g. from rain) and tending to wash away any grimeor other contaminants that have not been destroyed by the photocatalyticactivity of the surface.

[0030] Preferably, the coated glass has a haze of 1% or lower, which isbeneficial because this allows clarity of view through a transparentcoated substrate.

[0031] The invention is further illustrated by the following Examples,in which gas volumes are measured at standard temperature and pressureunless otherwise stated. The thickness values quoted for the layers weredetermined using high resolution scanning electron microscopy (SEM)and/or Xray photoelectron spectroscopy (XPS) depth profiling. XPS wasalso used to provide information on the surface and bulk elementalcomposition of the coatings.

[0032] The transmission and reflection properties of the coated glasseswere determined using a Hitachi U-4000 spectrophotometer. The a, b andL* values mentioned herein of the transmission and/or reflection coloursof the glasses refer to the CIE Lab colours. The visible reflection(measured on the coated side unless otherwise stated) and visibletransmission of the coated glasses were determined using the D65illuminant and the standard CIE 2° observer in accordance with the ISO9050 standard (Parry Moon airmass 2) The haze of the coated glasses wasmeasured using a WYK-Gardner Hazeguard+haze meter.

[0033] The photocatalytic activity of the coated glasses was determinedfrom the rate of decrease of the area of the infrared peakscorresponding to C-H stretches of a stearic acid film on the coatedsurface of the glass under illumination by UVA light or sunlight. Thestearic acid film was formed on samples of the glasses, 7-8 cm square,by spin casting 20 μl of a solution of stearic acid in methanol(8.8×10⁻³ mol dm⁻³) on the coated surface of the glass at 2000 rpm for 1minute. Infra red spectra were measured in transmission, and the peakheight of the peak corresponding to the C-H stretches (at about 2700 to3000 cm⁻¹ ) of the stearic acid film was measured. The photocatalyticactivity is expressed in this specification as t_(90%) (in units of min)which is the time of UV exposure taken to reduce the peak height by 90%(i.e. down to 10% of its initial value). For measurement ofphotocatalytic activity, the coated side of the glass was illuminatedwith a UVA lamp (UVA-351 lamp obtained from the Q-Panel Co., Cleveland,Ohio, USA) having a peak wavelength of 351 nm and an intensity at thesurface of the coated glass of approximately 32 W/m² or by sunlightoutside on a clear sunny day in June at Lathom, Lancashire, England.

[0034] The static water contact angle of the coated glasses wasdetermined by measuring the diameter of a water droplet (volume in therange 1 to 5 μl) placed on the surface of the coated glass as produced,or after irradiation of the coated glass using the UVA 351 lamp forabout 2 hours (or as otherwise specified).

[0035] Abrasion testing of the coated glass was in accordance with BS EN1096, in which a sample of size 300 mm×300 mm is fixed rigidly, at thefour corners, to the test bed ensuring that no movement of the sample ispossible. An unused felt pad cut to the dimensions stated in thestandard (BS EN 1096 Part 2 (1999)) is then mounted in the test fingerand the finger lowered to the glass surface. A load pressure on the testfinger of 4N is then set and the test started. The finger is allowed toreciprocate across the sample for 500 strokes at a speed of 60strokes/min±6 strokes/min. Upon completion of this abrasion the sampleis removed and inspected optically and in terms of photocatalyticactivity.

[0036] Humidity testing of the coated glasses comprised temperaturecycling the coated glass from 35° C. to 75° C. at 100% relativehumidity.

[0037] In Examples 1 to 10 coatings were deposited on stationary glasssamples by chemical vapour deposition.

[0038] In Examples 11 to 59 and Comparative Examples A to D, a ribbon offloat glass was coated with a two-layer coating as the ribbon advancedover the float bath during the float glass production process. The glassribbon was coated at the edge across a width of approximately 10 cm.

[0039] Layer 1 (the first layer to be deposited on the glass) was alayer of silicon oxide. Layer 1 was deposited by causing a gaseousmixture of coating precursors to contact and flow parallel to the glasssurface in the direction of movement of the glass using coatingapparatus as described in GB patent specification 1 507 966 (referringin particular to FIG. 2 and the corresponding description on page 3 line73 to page 4 line 75).

[0040] Layer 2 (the second layer to be deposited) was a layer comprisingtitanium dioxide. Layer 2 was deposited by combining separate gasstreams comprising titanium tetrachloride in flowing nitrogen carriergas, ethyl acetate (EtOAc) in flowing nitrogen carrier gas, tintetrachloride in flowing nitrogen or dimethyl tin dichloride (DMT) inflowing nitrogen and a bulk flow of nitrogen into a gaseous mixture andthen delivering the gaseous mixture to the coating apparatus where itcontacted and flowed parallel to the glass surface. Titaniumtetrachloride, tin tetrachloride or DMT and ethyl acetate were entrainedin separate streams of flowing nitrogen carrier gas by passing nitrogenthrough bubblers.

[0041] Table 1 describes the general deposition conditions used for theseries of Examples and Comparative Examples, 11 to 18, 19 to 24, 25 to59 and A to D.

[0042] In Examples 60 to 66, two-layer coatings were applied by on lineCVD to a float glass ribbon across its full width of approximately 132inches (3.35m) in the float bath during the float glass productionprocess.

[0043] The two layer coating consisted of a silicon oxide layerdeposited first on the float glass ribbon and tin containing titaniumoxide layer deposited on to the silicon oxide layer.

[0044] Titanium tetrachloride (TiCl₄) and ethyl acetate were entrainedin separate nitrogen carrier gas streams. For the evaporation of TiCl₄ athin film evaporator was used. The TiCl₄ and ethyl acetate gas streamswere combined to form the gaseous mixture used to deposit the titaniumoxide layer. This mixing point was just prior to the coater.

[0045] Table 2 describes the general deposition conditions used forExamples 60 to 66. In Table 2, slm means standard liters per minute andsccm means standard cc per minute. TABLE 1 Examples 25 to 59 ExamplesExamples Comparative 11 to 18 19 to 24 Examples A to D Linespeed 135m/hr 150 m/hr 150 m/hr Glass Temperature at ˜630° C. ˜630° C. ˜630° C.TiO₂ Coater Glass Temperature at   710° C.   725° C.   695° C. silicacoater Silica Undercoat Conditions SiH₄  24 cc/min  80 cc/min  80 cc/minN₂  81/min  81/min  81/min C₂H₄ 144 cc/min 480 cc/min 240 cc/min O₂  48cc/min 160 cc/min  80 cc/min TiO₂ Conditions TiCl₄ Bubbler    50° C.  50° C.   50° C. Temperature N₂ to TiCl₄ Bubbler 125 cc/min 175-200125-175 cc/min cc/min EtOAc Bubbler    35° C.    35° C.    35° C.Temperature N₂ to EtOAc Bubbler 125 cc/min 175-200  90-210 cc/min cc/minBulk N₂ 101/min 101/min 101/min Precursors Used SnCl₄ SnCl₄ SnCl₄ or DMT

[0046] TABLE 2 Examples 60 to 66 Linespeed 477 inches/min (727 m/hr)Glass Temperature at TiO₂ Coater 680° C.-700° C. Silica UndercoatConditions (at each of two coaters, temperatures approximately 721° C.and 690° C.) SiH₄  2.3 slm N₂  285 slm He  250 slm C₂H₄   12 slm O₂   8slm TiO₂ Topcoat Conditions TiCl₄   10 sccm EtOAc 26.7 sccm Bulk He  300slm Bulk N₂  300 slm DMT Precursor 1.5 g/min to 4 g/min

[0047] Typical conditions for delivery of the tin precursors frombubblers for the Examples are described in Table 3. TABLE 3 Flow ratesof Bubbler Bubbler Nitrogen Precursor Delivery Temperature carrier gasDimethyltin Blow approx. 140° C. 0-250 Dichloride- nitrogen cc/min DMTthrough molten solid Tin (IV) Blow approx. 70° C.  0-700 Chloride-nitrogen cc/min SnCl₄ through liquid

EXAMPLES 1 TO 10

[0048] In Examples 1 to 10 coatings having a two layer alkali ionblocking coating (comprising a tin oxide layer at the glass surface anda silica layer on the tin oxide layer) were deposited on to stationaryglass substrates using a laboratory CVD reactor. Titania coatings weredeposited using bubblers containing TiCl₄ and ethyl acetate (EtOAc) at aTiCl₄:EtOAc molar ratio of about 1:3. The deposition conditions were setso as to give 12%-16% visible reflection. General deposition conditionsused for Examples 1 to 10 are described in Table 4. TABLE 4 TiCl₄Bubbler  65° N₂ to TiCl₄ 50 to 200 ce/min Temperature Bubbler EtOAcBubbler  45° N₂ to EtOAc 75 to 200 cc/min Temperature Bubbler SubstrateTemperature 660° C. Bulk N₂ 8.5 l/min (Susceptor Reading) Temperature of180- Coating Period 10-15 seconds Delivery Lines 200° C.

[0049] Examples 1 to 10 were deposited using a SnCl₄ delivery range of 0to 120 cc/min nitrogen to the SnCl₄ bubbler (corresponding to about0-0.4 g/min).

[0050] The specific deposition conditions for Examples 1 to 10 aredescribed in Table 5 together with t₉₀% for each of the depositedcoatings. There was appreciable scatter in the measurements of t₉₀%.Some of this scatter can be explained by a varying film thickness causedby variations in the deposition conditions (e.g. a SnCl₄ bubblertemperature of lower than 35° C. and modified carrier gas flows to TiCl₄and EtOAc bubblers).

[0051] XPS depth profiling indicated the coatings to be approximately700 Å thick. Tin was detected throughout the containing coatings at alevel of 0.3 atom. % for coatings deposited at 0.08 g/min SnCl₄. TABLE 5N₂ Flow Rate to Bubbler Example TiCl₄ (cc/min) EtOAc (1/min) SnCl₄(cc/min) t_(90%) (min) 1 100 130 20 62 2 140 140 20 55 3 200 200 50 90 4100 100 20 98 5 120 100 120 123 6 140 140 20 48 7 50 100 50 80 8 50 10050 84 9 60 100 60 151 10 75 75 75 55

Example 11 to 18

[0052] Examples 11 to 18 were deposited by on line CVD during the floatglass production process, at a TiCl₄:EtOAc molar ratio of 1:3 and at arelatively low precursor flow (0-0.4 g/min SnCl₄). All coatings weredeposited on to the silica undercoat and were optimised to give 12-16%visible reflection. The general coating conditions were as described inTable 1 above, the specific coating conditions for each of Examples 11to 18 are described in together with t₉₀%, the visible reflection andthe contact angle (static water contact measured after exposure toultraviolet light (UVA lamp). TABLE 6 Nitrogen carrier gas flow rates tobubbler Visible TiCl₄ EtOAc SnCl₄ Reflection Contact Example (cc/min)(cc/min) (cc/min) t_(90%) (min) (%) Angle (°) 11 150 150 20 50.5 17.2729 12 150 150 40 60 18.16 14.3 13 150 150 60 127.5 18.85 18.7 14 150 15080 111 19.26 12.1 15 150 150 100 110 19.19 19.2 16 110 110 100 103 13.6410.6 17 110 110 50 67.5 13.24 12.9 18 110 110 20 77 13.4 22.2

[0053] The coatings of Examples 11 to 18 passed a salt spray test,remaining unchanged after 830 hours. Humidity testing of the coatingsfor Examples 11 to 19 was carried out, the coatings remained unchangedafter 200 cycles (the maximum number of cycles performed). In contrast,undoped titania coatings deposited under similar conditions survivedonly 17 cycles of the humidity test before failing at the SiO₂/TiO₂interface.

[0054] Abrasion testing on the Examples 11 to 18 showed that tincontaining titania coatings were more robust than the undoped TiO₂ (tovisual examination).

Examples 19 to 24

[0055] Examples 19 to 24 were deposited by on line CVD during the floatglass production process as described in Table 1 above at a relativelyhigh precursor flow (0-2.8 g/min SnCl₄). The specific coating conditionsfor each of Examples 19 to 24 are described in Table 7. The static watercontact angle before and after UVA exposure (for approximately 2 hours,the contact angle after UVA exposure is in brackets), t₉₀% using the UVAlamp and t_(90%) using sunlight are described in Table 8. TABLE 7 N₂ toTiCl₄ N₂ to EtOAc N₂ to SnCl₄ Example (cc/min) (cc/min) (cc/min) 19 175175 25 20 175 175 50 21 175 175 75 22 175 175 300 23 175 175 500 24 175175 700

[0056] TABLE 8 Contact angle before t_(90%) t_(90%) Example (after) UVAexposure (min) UVA (min) sunlight 19 43.4 (3.6)  95 129.5 20 17.8 (7)  105.5 221 21 28.8 (3.6)  165.5 262.5 22 40.9 (11.5) 116 230 23   4(3.3)  102 154 24 7.6 (4.5) 139 181.5

[0057] The haze, visible transmission, visible reflection and thetransmission and reflection colours of Examples 19 to 24 are describedin Table 9. TABLE 9 Transmission Reflection Example Haze % L* a* b* % L*a* b* 19 0.09 84.5 93.7 −1 4.4 15.1 45.7 0.6 −12.3 20 0.2 82.5 92.8 −15.3 16.3 47.4 0.6 −13.1 21 0.13 82.9 93 −1 5.1 15.8 46.7 0.6 −12.8 220.22 82.6 92.9 −1 5.3 17 48.2 0.5 −13.4 23 0.21 79.8 91.6 −0.9 6.2 18.449.9 0.4 −13.7 24 0.45 81.1 92.2 −0.9 5.4 17.6 49 0.2 −12.6

[0058] Tin concentration within the titania coatings was measured usingXPS depth profiling for some Examples and the results are described inTable 10 for particular delivery rates of tin chloride. TABLE 10 TiO₂Surface Tin Bulk Tin Thickness Concentration Concentration Example (Å)(atom %) (atom %) 17 119 0.8 0.1 20 207 0.9 0.1 15 215 1.1 0.2 23 2592.1 0.4 24 283 4.3 1.2

[0059] Tin was found to be segregated at the top surface with lowerlevels of tin present in the body of the TiO₂.

Examples 25 to 59 and Comparative Examples A to D.

[0060] Examples 25 to 59 and Comparative Examples A to D were depositedby on line CVD during the glass production process as described above inTable 1. Tin chloride was used as the tin precursor in Examples 25 to40, DMT as the tin precursor in Examples 41 to 59. No tin precursor wasused in the Comparative Examples. The specific coating conditions andvisible reflection for Examples 25 to 40 are described in Table 11, forComparative Examples A to D in Table 12 and for Examples 41 to 59 inTable 13. In each of the Examples 25 to 59 and Comparative Examples A toD, the nitrogen make up was 10 l/min. TABLE 11 N₂ to N₂ to TiCl₄ EtOAcN₂ to SnCl₄ EtOAc:TiCl₄ Visible Examples (cc/min) (cc/min) (cc/min)Ratio Reflection (%) 25 175 130 10 3 25.15 26 175 130 30 3 26.21 27 175130 50 3 25.92 28 175 130 70 3 26.41 29 175 130 100 3 26.51 30 175 210100 5 23.5 31 175 210 70 5 23.58 32 175 210 50 5 23.71 33 175 210 30 523.55 34 175 210 10 5 22.69 35 175 175 10 4 24.42 36 175 175 30 4 25.337 175 175 50 4 25.61 38 150 150 30 4 21.16 39 125 125 30 4 19.2 40 17590 30 2 29.47

[0061] TABLE 12 Comparative EtOAc:TiCl₄ Visible Examples N₂ to TiCl₄ N₂to EtOAc Ratio reflection (%) A 250 170 3 19.26 B 250 280 5 17.2 C 250110 2 26 D 175 175 4 13.79

[0062] TABLE 13 Visible N₂ to EtOAc:TiCl₄ reflection Examples N₂ toTiCl₄ EtOAc N₂ to DMT Ratio (%) 41 175 130 10 3 14.67 42 175 130 30 319.13 43 175 130 50 3 19.48 44 175 130 70 3 19.21 45 175 130 100 3 18.946 175 210 100 5 16.76 47 175 910 70 5 17.9 48 175 210 50 5 18.54 49 175210 30 5 19.29 50 175 210 10 5 18.7 51 175 90 10 2 23 52 175 90 30 223.5 53 175 90 50 2 23 55 175 90 100 2 22.14 56 175 175 30 4 20.36 57175 175 50 4 20.13 58 175 175 70 4 20.05 59 175 130 260 3 18

[0063] The coated glasses of Examples 24 to 59 and Comparative ExamplesA to D were tested for durability using the European surface #1 abrasiontest (i.e. European standard abrasion test). Coatings were abraded for500 strokes and t₉₀%, and the static water contact angle (to determinethe hydrophilic nature of the surface) were measured before and afterabrasion and the coatings were examined visually after abrasion.

[0064] Values of t₉₀% before and after abrasion and contact angle beforeand after abrasion (the values after abrasion are in brackets) togetherwith the results of visual examination (visual) and examination as tothe hydrophilicity (hydro) after abrasion of the coatings for Examples25 to 40 are described in Table 14, for Comparative Examples A to D inTable 15 and for Examples 41 to 59 in Table 16. The static water contactangles were determined after exposure to sunlight for 24 hours. Theresults of visual examination and examination as to the hydrophilicityof the coatings after abrasion are reported in accordance with the key:Visual, 1=No Damage, 2=Damage, 3=Coating Removed; hydrophilicity, 1hydrophilic, 2=slightly patchy, 3=patchy, 4=fail. TABLE 14 AbrasionContact Angle Result t_(90%) before and (after) before and (after)Examples Visual Hydro abrasion abrasion 25 2 1 12.1 (19.7) 26 1 1  72(121)  5.4 (14.4) 27 1 1  69 (73)  6.4 (6.4) 28 1 1  76 (177) 12.4(21.4) 29 1 1  84 (43)  3.4 (24.1) 30 1 2 121 (200)   8 (6.2) 31 1 1  90(97) 22.2 (17.7) 32 1 1  67 (127)  7.2 (24.5) 33 1 1  94 (132)  5.4(5.4) 34 1 2  42 (95)   8 (11.5) 35 1 1  84 (889) 13.5 (19.5) 36 1 1  47(103)   3 (3) 37 1 1  58 (97)  6.6 (5.8) 38 1 1 130 (128) 33.2 (14.9) 391 1  68 (91)  1.8 (8.4) 40 1 1 134 (1109)  3.7 (12.5)

[0065] TABLE 15 Compara- Abrasion Contact Angle tive Result t_(90%)before and (after) before and (after) Examples Visual Hydro abrasionabrasion A 2.5 4  11 (2210)  5.7 (26) B 2.5 2  91 (1430)  3.4 (24.5) C2.5 1  17   8 (28.4) D 2.5 2 114 10.4 (18.4)

[0066] TABLE 16 Abrasion Contact Angle Result t_(90%) before and (after)before and (after) Examples Visual Hydro abrasion abrasion 41 1 1   43(1275) 11.6 (8.1) 42 1 1   41 (1169)  9.9 (10.6) 43 1 3   38 (160) 13.7(23.9) 44 1 1   40 (220) 14.7 (7) 45 1 1   38 (27)  4.6 (15.9) 46 1 1  39 (32) 10.2 (10.2) 47 1 1 54.5 (188)  6.3 (6) 48 1 1   42 (39) 11.9(14.5) 49 1 1   50 (1085) 15.1 (14.4) 50 1 1   76 (1055) 27.9 (20.9) 512 2   19 (975) 33.2 (21.6) 52 1 1   30 (1095)  5.4 (18.1) 53 1.5 1   90(31) 18.6 (26.4) 55 1 1   32 (295)  9.9 (8.4) 56 1 1   42 (2350) 15.1(11.5) 57 1 1   51 (82)  7.8 (6.7) 58 1 1   86 (1110) 17.5 (17.3) 59 1 3  38 (99) 10.4 (26)

[0067] XPS analysis of the tin containing coatings indicated tinsegregation at the surface of the coating with a lower tin contentmeasured in the bulk of the titania coating. This was observed with bothSnCl₄ and DMT. Summary measurements are shown in Table 17 below. TABLE17 Surface tin Bulk tin Tin Precursor flow EtOAc:TiCl₄ concentrationconcentration rate Molar Ratio (atom %) (atom %) 0.12 g/min SnCl₄ 3:10.4 to 0.9 0.1 0.28 g/min SnCl₄ 3:1 0.7 to 1.2 0.1 to 0.3 0.28 g/minSnCl₄ 5:1 0.6 to 1.2 0.1 to 0.4 0.12 g/min DMT 3:1 0.8 to 1.5 0.1 to 0.3

Examples 60 to 66

[0068] Examples 60 to 66 were deposited by on line CVD during the floatglass production process across the full width of a float glass ribbonas described above in Table 2. DMT was used as the tin precursor. Theflow rates of DMT used for each of the Examples 60 to 66 are describedin Table 18, together with values of t_(90%) and static water contactangle before and after 500 abrasion strokes in accordance with theEuropean standard abrasion after abrasion are in brackets). TABLE 18Contact Angle DMT flow t_(90%) before and (after) before and (after)Example (cc/min) abrasion abrasion 60 2.5 30 (1240) 21.1 (21.1) 61 5 51(1240) 14.7 (13) 62 7.5 31 (560)  6.7 (8.2) 63 10 25 (2540)  7.9 (13.1)64 12.5 87 (1240)  6.4 (6.6) 65 15 70 (1280)   16 (16) 66 20 50 (1630)20.3 (17.5)

[0069] t_(90%) was measured after the coatings were exposed to sunlightfor 24 hours.

[0070] Examination by scanning electron microscopy (SEM) showed thatafter abrasion, coatings with no tin were highly furrowed and manyparallel abrasion marks were scored into the surface of the coating.There was also a small loss in coating thickness. By comparison tincontaining coatings were marked less, there was no significant loss inthickness, and the coating surface appeared smooth.

[0071] The optical properties of the coatings were investigated beforeand after abrasion. The visible transmission and transmission colours ofthe Examples 60 to 66 are described in Table 19, the visible reflectionand colours in reflection are described in Table 20 (in Table 19 andTable 20 the values after abrasion are in brackets). TABLE 19 VisibleTransmission L* before and a* before and b* before and before and(after) (after) abrasion (after) abrasion (after) abrasion Exampleabrasion (%) (transmission) (transmission) (transmission) 60 85.8 (85.2)94.2 (94) −1.1 (−1.1)   3 (3) 61   86 (85.6) 94.3 (94.1) −1.1 (−1.1) 2.9(2.7) 62 84.1 (83.8) 93.5 (93.3) −1.1 (−1.1) 3.7 (3.6) 63 84.8 (84.6)93.8 (93.7) −1.1 (−1.1) 3.4 (3.2) 64 84.6 (84.7) 93.7 (93.8) −1.1 (−1.1)3.6 (3.2) 65 85.1 (84.3) 93.9 (93.6) −1.1 (−1.1) 3.4 (3.4) 66 84.1(83.9) 93.5 (93.4) −1.1 (−1.1) 3.8 (3.6)

[0072] TABLE 20 Visible Reflection L* before and a* before and b* beforeand before and (after) (after) abrasion (after) abrasion (after)abrasion Example abrasion (%) (reflection) (reflection) (reflection) 6013.3 (13.1) 43.2 (43) 0.4 (0.3)   −10 (−8.7) 61 12.6 (12.9) 42.2 (42.6)0.4 (0.3)  −8.4 (−8.1) 62 14.9 (15.2) 45.4 (45.9) 0.4 (0.4) −11.2 (−10)63   14 (13.8) 44.2 (44) 0.3 (0.3) −10.4 (−8.9) 64   14 (14.1) 44.2(44.4) 0.4 (0.4) −10.6 (−9.3) 65 13.8 (14.1)   44 (44.4) 0.3 (0.3) −10.8(−9.3) 66 14.9 (14.8) 45.5 (45.3) 0.3 (0.4) −11.3 (−9.8)

[0073] The coatings were analysed by XPS profiling and the results ofXPS of the thickness of the silica undercoat and the titania layer,together with the surface and bulk elemental analyses for tin andcarbon, are described in Table 21. TABLE 21 SiO₂ Surface Bulk UndercoatTiO₂ Composition Composition Thickness Thickness (atom %) (atom %)Example (Å) (Å) Sn C Sn C 60 293 242 0.2 34.0 0.07 8.7 61 293 220 0.311.6 0.12 2.8 62 293 242 0.5 18.0 0.06 2.6 63 293 242 0.4 16.9 0.05 1.464 297 255 0.5 47.1 0.13 11.2 65 300 242 0.6 17.3 0.12 1.7 66 375 3520.5 33.2 0.13 8.2

1. A-process for the production of a durable photocatalytically activeself-cleaning coated glass comprising contacting the surface of a hotglass substrate with a fluid mixture comprising titanium chloride, asource of oxygen and a tin precursor thereby depositing a tin containingtitanium oxide coating on the surface of the glass substrate.
 2. Aprocess as claimed in claim 1 wherein at least part of the fluid mixturecontacts the surface of the glass substrate by flowing over the glasssurface.
 3. A process as claimed in either claim 1 or claim 2 whereintitanium chloride comprises titanium tetrachloride.
 4. A process asclaimed in any of the preceding claims wherein the tin precursorcomprises a tin halide.
 5. A process as claimed in claim 4 wherein thetin halide comprises a tin chloride.
 6. A process as claimed in claim 5wherein the tin chloride comprises dimethyl tin dichloride or tintetrachloride.
 7. A process as claimed in any of the preceding claimswherein the source of oxygen comprises an ester.
 8. A process as claimedin claim 7 wherein the ester comprises a carboxylic acid ester.
 9. Aprocess as claimed in claim 8 wherein the carboxylic acid estercomprises a C₁ to C₄ acetate.
 10. A process as claimed in claim 9wherein the C₁ to C₄ acetate comprises ethyl acetate.
 11. A process asclaimed in any of the preceding claims wherein the glass substratecomprises a soda-lime-silicate glass substrate.
 12. A process as claimedin claim 11 further comprising depositing an alkali blocking underlayeron the surface of the glass substrate before depositing the tincontaining titanium oxide coating.
 13. A process as claimed in any ofthe preceding claims wherein the fluid mixture comprises a gaseousmixture.
 14. A process as claimed in any of the preceding claims whereinthe hot glass substrate is at a temperature in the range 500° C. to 750°C.
 15. A process as claimed in claim 14 wherein the hot glass substrateis at a temperature in the range 570° C. to 650° C.
 16. A process asclaimed in any of the preceding claims wherein the process is performedduring the float glass production process.
 17. A process as claimed inclaim 16 wherein the process is performed in the float bath.
 18. Aprocess as claimed in any of the preceding claims wherein the amount oftin in the bulk of the tin containing titanium oxide coating is below 10atom %.
 19. A process as claimed in claim 18 wherein the amount of tinin the bulk of the tin containing titanium oxide coating is below 5 atom%.
 20. A process as claimed in claim 19 wherein the amount of tin in thebulk of the tin containing titanium oxide coating is below 2 atom %. 21.A process as claimed in any of the preceding claims wherein there is agreater atomic percent tin in the surface of the tin containing titaniumoxide coating than there is in the bulk of the coating.
 22. A process asclaimed in claim 21 wherein the atomic percent tin in the surface of thetin containing titanium oxide coating is at least twice that in the bulkof the coating.
 23. A process for depositing a tin containing titaniumoxide coating on the surface of a hot glass substrate comprisingcontacting the surface of the glass substrate with a fluid mixturecomprising a titanium precursor, a source of oxygen and a tin precursorcharacterised in that the amount of tin in the bulk of the tincontaining titanium oxide coating is below 10 atom %.
 24. A coated glassproduced by a process as claimed in any of the preceding claims.
 25. Adurable, photocatalytically active coated glass comprising a glasssubstrate having a coating comprising tin containing titanium oxide, theamount of tin in the bulk of the coating being below 10 atom %.
 26. Adurable photocatalytically active coated glass as claimed in claim 25wherein the atomic percent tin in the surface of the coating is at leasttwice that in the bulk of the coating.
 27. A process substantially ashereinbefore described with particular reference to the Examples 1-66.